Potentiometer apparatus



April 9, 1968 R. L.. FERRE| 3,377,606

POTENTI OMETER APPARATUS Filed March 2, 1964 2 Sheets-Sheet l.

BY l

April 9, 1968 R. l.. FERRELL 3,377,606

POTETIOMETER APPARATUS Filed March 2, 1964 2 Sheets-Sheet 2 INVENTOR. Revu* L, Warn BY United States Patent O 3,377,606 POTENTIOMETER APPARATUS Robert L. Ferrell, Riverside, Calif., assignor to Spectrol Electronics Corporation, San Gabriel, Calif., a corporation of Delaware Filed Mar. 2, 1964, Ser. No. 348,598 Claims. (Cl. 338-174) This invention relates to variable resistors, and particularly to a potentiometer in which the components thereof are housed in a sealed unit which may be made small in size while retaining good performance capability.

As a result of widespread developments in automatic control apparatus, and other complex electrical systems, considerable demand exists for potentiometers as a means of providing a Variable voltage ratio. One common basic form of potentiometer employs a resistance element which may be connected across a source of electrical potential so that each point along a contact path on the resistance element provides a different voltage. Various wiper arrangements are then used to contact the resistance element at different points under the control of a rotary shaft or other adjusting means.

Conventionally, in one class of potentiometer-s the operating structure is contained in a housing which protects it from environmental conditions such as humidity, foreign particles, and the like, and provides electrical isolation. For example, plastic housings have been widely used to encase the electrical components of potentiometers. Normally, the potentiometer housing has some form of opening through which an adjusting member passes. The adjusting member is then connected to a wiper so that it can be moved to cause the wiper to variously contact the resistance element. A seal between the housing and the adjusting member may be accomplished by various arrangements to complete the closure of the housing.

Prior potentiometers, as described above, though highly developed, still present certain problems. For example, the considerable demand for potentiometers necessitates high volume production techniques; therefore, any simplification of the structure enabling more efficient production is truly a significant advance. This consideration is particularly true in view of the great demand for diminutive potentiometers which often present additional manufacturing difiiculties. That is, the increasingly smaller space alloted potentiometers in many systems creat manufacturing problems. These problems in turn cause the number of rejected potentiometers to increase and the price per acceptable unit to increase. As a result, potentiometers of small size with good performance capability are quite expensive. Therefore, a need exists for a potentiometer structure that is economical to manufacture, and which has good peformance capability. One aspect of this need is for a potentiometer in which the housing occupies little space so that the component parts thereof can be larger and more effective. Furthermore, simplification of required structure to provide a housing closure seal as well as a seal between .the rotary member and the housing along with any simplification in the structure which is not accompanied by compromise in operational characteristics would satisfy a significant need.

Prior art structures have necessitated manufacturing techniques vrequiring the use of epoxy resins to effect housing seals and to retain various c-omponents in place. Epoxy resin must be applied by hand Ioperation and thus the effectiveness of the seal is dependent upon the ability of the assembly personnel. Furthermore, many personnel have been found to be allergic to epoxy resin. Therefore, elimination of epoxy resin or -other adhesives .from potentiometers would constitute a significant advance in the art. Accordingly, an object of the present invention is to provide an improved variable resistance unit.

Another object of the present invention is to provide a potentiometer that is economical to manufacture, yet which has good performance characteristics.

Still another object of the present invention is to provide an economical potentiometer which has good heat dissipation capability, incorporate-s a relatively large resistance element, and has internal components effectively encased in a sealed housing.

A further object of the present invention is to provide an encased potentiometer unit that requires no separate sealing member between the adjustment shaft and the hou-sing, and requires no adhesive for assembly or closure sealing.

Still a further object of the present invention is to provide a potentiometer incorporating a housing which is sufficiently ductile to be crimped to lock the unit together; and which has a resiliently deformable, insulating surface to provide contacting support for electrical elements as Well as .to provide seals for both the adjusting member and the housing closure.

In accordance with a broad aspect of the present invention a resistance element is seated within a cavity formed by a housing having a base member and a cover member. Contact means slidably movable along the resistance element by an adjusting means is disposed within the cavity. A resiliently deformable means is disposed between the cover and base members and effects a housing closure seal.

In accordance with a more specific aspect, the present invention comprises a potentiometer, including a resistance element which is variously contacted by a wiper. The resistance element is seated on an electrically nonconductive surface of a lbase which may also support electrical terminal pins. A rotary adjustment shaft is also seated on the base and is mechanically connected to variously position the wiper as it is driven. A dluctile housing, eg. metal, with an internal coating of resiliently deformable material, e.g. rubber, is deformed and locked to the base. The rotary adjustment shaft passes through an opening in the housing with a seal therebetween accomplished by a portion of the coating. Furthermore, the coating engages the resistance element, holding it in position without the need for adhesives. As a result, the unit is sealed, tightly and effectively by a simple structure, with essentially no compromise in performance.

The structure of the invention, and other objects and advantages thereof will become apparent from a consider ation of the following description taken in conjunction with the accompanying drawings, in which:

FIG. l is a perspective view of a potentiometer of the present invention;

FIG. 2 is an exploded view of the potentiometer of FIG. l;

FIG. 3 is a sectional view along line 3 3 of FIG. l;

FIG. 4 is a sectional view along line 4 4 of FIG. 3;

FIG. 5 is a sectional view along line 5 5 of FIG. 3; and

FIG. 6 is a sectional view along line 6 6 of FIG. 5.

A variable resistor constructed in accordance with the lpresent invention may have any geometric configuration desired such as square, rectangular, round, Vor the like. Also the variable resistor may utilize any adjusting means desired such as a lead screw, -a worm gear, a single turn rotor, pressure transducers, or the like. However, for purposs of clarity of illustration and ease of description only the present invention will be described hereinafter with respect to a single turn, direct drive, trimmer potentiometer.

Referring initially to FIG. l, there is shown a housing 10 containing a resistance element 12 which takes the form of a wire-wound C-shaped member concentrically mounted therein. It should be expressly understood that the resistance element 12 may take any form or construction desired. The resistance element 12 may be variously engaged along a contact path by a rotary carriage or wiper assembly 14, to tap various voltages from the resistance element 12. The housing is formed by a base 16 and a cover 18. The cover 18 includes Ia back 20, of ductile material, such as metal, the interior surface of which carries a resiliently deformable layer 22, such as a rubberlike material. In one application, silicone rubber integrally formed as by being molded to a metalback 20 has functioned very satisfactorily.

The annular lower edge 24 of the cover 18 is deformed as by being crimped to lock the cover to the base 16, to form a housing closure seal as a result of the layer 22. Furthermore, the layer 22 engages the coil 12, holding it in position, and also contacts adjusting means such as a rotary shaft 26 to accomplish a seal therewith. In the cover structure, the layer 22 provides a true voltage break-down barrier, while the metal back results in good heat dissipation and avoids hot spots in the resistance element. Furthermore, the cover is relatively thin so that better space utilization is possible within the unit, and the resistance element 12 may be relatively large.

Considering the disclosed embodiment of the invention in greater detail, the circular, electrically non-conductive base 16 may be molded of plastic with the terminal pins 28, 29 and 30 fixed in the bottom 32 as shown in FIG. 3. Above the circular at surface 34 of the base, from which the pins extend, the base includes an outwardly-fiared annular lip 36, the interior of which forms a shoulder 38 on which the coil 12 is seated to be held in position by the circular cover 18.

The resistance element 12 is electrically contacted by terminal tabs 42 and 44 (FIG. 5) which are of thin metal shaped to lie primarily in an annular groove 46 (FIG, 3) in the base 16 inside the shoulder 38. The inner ends of the'terminal tabs 42 and 44 are affixed to the pins 29 and above which they lie as shown in FIG. 5 to form electrical contact therewith. The outward ends of the terminal tabs 42 and 44 lie in spaces 48 and 50 respectively, `below the ends of the resistance element 12 to establish a connection thereto. The arrangement of the terminal tabs 42 and 44 to engage the resistance element 12 is illustratd in the enlarged section of FIG. 6, which shows the connection between the terminal tab 44 and the resistance element 12.

The wiper contact 52 (FIG. 2) is part of a rider 54 having a central `bore 56, through which a center post 58 (FIG. 3) passes, so that the rider is supported on a shoulder 60 which also holds a collector 62 (FIG. 2). The rider 54 is of thin metal, formed with a central ring 59 containing the bore 56, carrying diametrically opposed arms 61 and 63 extending therefrom. The arm 61 terminates in the contact 52 While the arm 63 serves to lock the rider 54 to the rotative shaft 66.

Both the rider 54 and the shaft 66 are rotatively positioned on the post 58, which is yan integral part of the base 16, concentrically rising above a disk section 65 in the interior center of the base, the upper surface of which forms the shoulder 68, upon which the collector 62, the rider 54 and the shaft 66 are stacked.

The collector 62 has an extending tab 64 that drops into the groove 46 and is affixed to the pin 28. Thus, the collector 62 firmly engages the rider 54 on the post 58 to establish electrical connection between the pin 28 and the wiper contact 52.

The rider 54 may be rotated to various positions by a shaft 66 to which it is affixed by a stop-lug 68 on the shaft 66 dwelling in a slot 70, and a spring 72 locking in a groove 74 (FIG. 2). That is, the arm 61 of the rider 54 receives the stop-lug 68 extending from the bottom of the shaft 66; while the arm 63 terminates in a spring 72 that snaps into the groove 74. In this manner, the rider is simply and effectively locked to the shaft 66.

The shaft 66 includes two sections integrally formed as a pair of stacked concentric disks 75 and 77, the upper surface 76 of which defines slot 78 for receiving an adjusting tool to position the wiper. The curved periphery of the lower disk 77 vconstrains the contact 52 as it is moved in a circular path. The annular internal corner 79 (FIG. 6) between the disks 75 and 77 receives an internally protruding ring section 88 integral with the layer 22 and which may be viewed yas an annular extension thereof having increased thickness. The ring section 80 provides effective packing gland sealing between the shaft 66 and the cover 18, yet the structure is exceedingly simple in manufacture and assembly.

In the manufacture of the disclosed structure, the base 16 may be formed with the terminal pins 28, 29 and 3f) molded therein. Next the tabs 42 and 44 (FIG. 2) may be affixed to resistance element 12 and the resistance element placed on shoulder 38 with the tabs 42 and 44 plaed in the groove 46 and aixed to the ends of their asosciated pins along with the tab 64 of the collector 62. These tabs and the collector may be stamp formed, along with the rider 54 which is affixed to the shaft 66 as a subassembly and then placed -on the post 58. Then, the cover 18, with the layer 22 and ring section 80 molded therein may be placed over the base, pressed downwardly to effect a seal about shaft 66 and provide good electrical conta-ct, as well as to retain the resistance element in place, yand the annular edge 24 crimped to lock and seal the housing. Prior to placing the cover 18 in position it may be advisable to apply some appropriate lubricant in the corner 'i9 to lubricate the moving parts. In manufacturing the -cover 18, nickel-silver alloy stampings with molded silicone rubber coatings have been found to provide a preferred embodiment.

In the operation of the potentiometer, as the shaft 66 is revolved on the post 58, the rider 54 is moved through a circular path to drive the contact 52 to variously engage the resistance element 12.

The shaft 66 may be rotated slightly less than one full revolution because of contact between the stop lug 68 on the shaft, and a mating stop member 81 (FIG. 4) radially extending into the annular groove 46. Of course, the placement of the stop-lug 68 and stop member 81 is such that as the shaft 66 completes the extent of its rotation, the contact 52 wipes essentially from one end of the resistance element 12 to the other providing the full range of operation.

An important feature of the structure resides in the consideration that it can be economically manufactured yet provide high quality performance.

Still another important feature resides in the relatively thin wall possible about the resistance element 12, with the result that a unit of specified size may house a resistance element having increased resistance range and improved resolution.

Although these and other important features of the present invention are apparent in the described embodiment of the invention, it will also be apparent that the present invention provides an apparatus capable of many variations and modifications, consequently the present invention is not to be limited to the particular arrangement shown and described, but rather shall be determined in accordance with the following claims.

What is claimed is:

1. A variable resistor comprising: a housing including a base member and a cover member and defining a cavity internally thereof; a resistance element seated within said cavity; contact means disposed within said cavity in sliding contact with said resistance element; adjusting means extending through said housing and adapted upon turning to impart movement to ,said contact means along said resistance element; terminal means electrically connected to said resistance element and said Contact means and extending through said housing; and resiliently compressible rubber-like material molded onto the inner surface of and forming an integral part of said cover member to form a housing closure seal between said cover member and said base member, and extending into surrounding engagement with said adjusting means to form a housing closure seal at the area where said adjusting means extends therethrough, said housing closure seals preventing entrance of foreign contaminants into said housing.

2. A variable resistor comprising: a housing including a base member and a metallic cover member and defining a cavity internally thereof; a resistance element seated within said cavity; contact means disposed within said cavity in sliding contact with said resistance element; adjusting means extending through said housing and adapted upon turning to impart movement to said contact means along said resistance element; terminal means electrically connected to said resistance element and said contact means and extending through said housing; and a layer of electrically insulative resiliently compressible material covering substantially the entire interior surface of said cover member and forming, when afiixed to said base member, a seal for said housing over the area of engagement between said base and cover members without the use of adhesives, and an insulating layer between said metallic cover member and said resistance element.

3. A variable resistor comprising: a housing including a base member and a cover member and defining a cavity internally thereof; a resistance element seated within said cavity; contact means disposed within said cavity in sliding contact with said resistance element; said cover member defining a centrally disposed aperture therein; adjusting means extending through said aperture and adapted upon turning to impart movement to said contact means along said resistance element; terminal means electrically connected to said resistance element and said contact means and extending through said housing; and a layer of electrically insulative resiliently compressible material sandwiched between and extending over the entire area of contact between said cover member and said base member and including a region of substantially increased thickness surrounding said adjusting means, said resiliently compressible material forming an integral part of said housing to effect a seal against the entrance of foreign contaminants into said housing at said area of contact and at said adjusting means.

4. A variable resistor in accordance with claim 3 wherein said region of increased thickness defines an annular extending ring which is compressed between said cover member and said adjusting member to form said seal.

5. A potentiometer, comprising: a housing including a base member having an electrically non-conductive internal surface; a resistance element seated loosely on said electrically non-conductive surface; terminal means connected to said resistance element and extending outside said housing for electrical connection thereto; contact means for variously engaging said resistance element; adjusting means extending through said housing and adapted upon turning to impart movement to said contact means along said resistance element; and a metal cover, the internal surface of which is covered with a layer of resiliently compressible electrically insulative material bonded thereto, said cover being affixed to said base member and said layer of material engaging said base member and forming therewith a housing closure seal, said layer of material further engaging said resistance element with a force sufficient to compress that part of said layer between said element and said cover to press element against said base member thereby to hold said resistance element fixed against said electrically non-conductive surface without the use of adhesives.

6. A potentiometer, comprising: a housing including a base member having an electrically non-conductive internal surface and a centrally disposed post extending upwardly therefrom; a resistance element loosely seated on said electrically non-conductive surface; terminal means connected to said resistance element and extending outside said housing for electrical connecLion thereto; a rotative member disposed upon said post and ha\ing a portion extending outside said housing for rotation thereof; contact means connected to said rotative member and movable thereby for variously engaging said resistance element; said housing further including a ductile cover aixed to said base member; the said portion of said rotative member extending through an aperture in said cover, and electrically insulative resiliently compressible layer of material molded onto the entire interior of said cover, and engaging said resistance element and pressing it against said base member to hold said element xed and having an area of increased thickness engaging said rotative member around said portion extending through said cover to provide a seal therewith against the entry of foreign contaminants.

7, A potentiometer according to claim 9 wherein said ductile cover is a cup-shaped metal member and is afiixed to said base member by being crimped about the periphery thereof to lock on said base member.

8. A potentiometer according to claim 9, wherein said ductile cover is metal and said rubber-like coating com prises silicone rubber covering said interior surface thereof.

9. A potentiometer, comprising: an electrically nonconductive base member defining a centrally disposed post extending upwardly therefrom and an outwardly flared upwardly extending lip defining a shoulder; a plurality of electrically conductive leads, spaced apart, integrally molded with and extending through said base member, a resistance element loosely seated on said shoulder; electrical connections between the ends of said resistance element and certain of said leads; a rotor means mounted on said post for rotation relative to said resistance element, said rotor means including a shaft of electrically non-conductive material, and an electrically conductive rider clamped thereto, which rider includes a contact to engage said resistance element; an electrical connection between said rider and one of said leads and a cover including a layer of ductile material and a layer of silicone rubber material formed integrally therewith over the entire interior surface thereof, said cover being inwardly deformed about the periphery thereof into engagement with said lip and is thereby aiiixed to said base member whereby said silicone rubber layer presses against said resistance element and is deformed thereby to retain said element fixed against said base member without adhesives.

10. A potentiometer as defined in claim 9 wherein said rotor means defines a downwardly depending lug and diametrically opposite said lug a groove in the periphery of said rotor means, said rider includes a first arm having said contact afiixed thereto and defining a slot therein for receiving said lug, and a second arm diametrically opposite said first arm and having an upwardly extending terminal end received in said groove thereby to clamp said rider to said rotor means.

UNITED STATES PATENTS 2,213,078 8/1940 Stoekle 338-174 X 2,309,798 2/ 1943 Stoekle et al 338-174 X 2,358,991 9/1944 Miller 338-184 X 2,406,503 8/ 1946 Miller 338-164 2,737,560 3/1956 Mucher 338-174 2,778,906 1/1957 Burgess 338-164 X 2,917,721 12/1959 Kelver et al. 338-164 3,197,727 7/1965 Hulbert 338-184 X 3,237,140 2/1966 Barden et al. 338--164 FOREIGN PATENTS 575,340 2/ 1946 Great Britain.

ANTHONY BARTIS, Primary Examiner. 

1. A VARIABLE RESISTOR COMPRISING: A HOUSING INCLUDING A BASE MEMBER AND A COVER MEMBER AND DEFINING A CAVITY INTERNALLY THEREOF; A RESISTANCE ELEMENT SEATED WITHIN SAID CAVITY; CONTACT MEANS DISPOSED WITHIN SAID CAVITY IN SLIDING CONTACT WITH SAID RESISTANCE ELEMENT; ADJUSTING MEANS EXTENDING THROUGH SAID HOUSING AND ADAPTED UPON TURNING TO IMPART MOVEMENT TO SAID CONTACT MEANS ALONG SAID RESISTANCE ELEMENT; TERMINAL MEANS ELECTRICALLY CONNECTED TO SAID RESISTANCE ELEMENT AND SAID CONTACT MEANS AND EXTENDING THROUGH SAID HOUSING; AND RESILIENTLY COMPRESSIBLE RUBBER-LIKE MATERIAL MOLDED ONTO THE INNER SURFACE OF AND FORMING AN INTEGRAL PART OF SAID COVER MEMBER TO FORM A HOUSING CLOSURE SEAL BETWEEN SAID COVER MEMBER AND SAID BASE MEMBER, AND EXTENDING INTO SURROUNDING ENGAGEMENT WITH SAID ADJUSTING MEANS TO FORM A HOUSING CLOSURE SEAL AT THE AREA WHERE SAID ADJUSTING MEANS EXTENDS THERETHROUGH, SAID HOUSING CLOSURE SEALS PREVENTING ENTRANCE OF FOREIGN CONTAMINANTS INTO SAID HOUSING 